The present invention relates to an apparatus and method for dispensing a liquid cryogen. More particularly, the present invention relates to such an apparatus and method in which the liquid cryogen is dispensed through a dispensing tube and the flow of liquid cryogen within the dispensing tube is inhibited or stopped by heating the dispensing tube to an extent that the liquid cryogen undergoes nucleate boiling within the dispensing tube.
Liquid cryogen is dispensed in a wide variety of industrial processes. For example, containers such as aluminum cans are pressurized by dispensing discrete amounts of nitrogen into the containers prior to their being sealed. A common approach for accomplishing such dispensing is to simply allow a stream of liquid nitrogen to fall into the cans (before sealing) as the cans are propelled along a conveyor. The problem with such dispensing is that liquid nitrogen is wasted and in order to ensure measured amounts of liquid nitrogen are deposited in each of the cans, the food processing line must travel at a constant rate.
An alternative approach for dispensing a liquid cryogen is to accurately meter the liquid cryogen. An example of a device designed to carry out such an approach is disclosed in European Patent Application 0 331 287 published Sep. 6, 1989. The device disclosed in this patent consists of a reservoir having an electrically heated dispensing tube connected to the bottom of the reservoir. Liquid cryogen contained within the reservoir is metered by an electrically controlled solenoid valve which, when activated, closes off the dispensing tube. The dispensing tube is electrically heated so that liquid cryogen within the dispensing tube undergoes film boiling. The film boiled liquid cryogen within the dispensing tube acts to lubricate slugs of liquid cryogen that are dispensed from the dispensing tube when the solenoid valve is raised.
As will be discussed, the Present invention provides an apparatus and method for dispensing cryogen that does not rely on conventional solenoid valves and the like to accomplish the dispensing of the liquid cryogen. Additionally, the dispensing apparatus and method of the present invention provide a flexibility in dispensing that is not present in the prior art.